Computers, digital switches, and other digital systems are becoming ever more present with the high technological boom of the late twentieth century. A vast majority of these digital systems utilize various types of circuit boards that are installed in a chassis of the digital system. The circuit boards typically contain circuitry that supplements system operations and aids in enhancing system performance.
Invariably it is necessary to replace circuit boards due to system upgrades or circuit board failures. The process of replacing (or swapping) a circuit board is carried out by extracting the circuit board from the digital system chassis, and replacing it with another circuit board. Originally systems had to be powered-down while inserting or removing a circuit board. System power-downs were necessary in order to prevent voltage spikes that could potentially damage the new circuit board. However, in applications that required non-stop operation, it was impracticable to power down the system in order to change circuit boards. Therefore, a method for installing or removing circuit boards during continuous system operation was needed.
In response to the need for non-stop system operation during circuit board replacement, "hot swap" circuit boards began to be developed. Hot swap circuit boards typically integrate "hot swap" circuitry which allows the digital system to remain powered during circuit board insertions or removals by controlling circuit board voltages during insertion and removal.
Traditional hot swap circuit boards control board voltage by using various methods. Such methods include the use of discrete logic, proximity sensors, and other types of electrical techniques. However, electrical methods for hot swap control have various drawbacks. Many hot swap circuit designs require power to be dissipated at all times during circuit board operation. This type of design places limitations on circuit board voltages and currents. Other hot swap designs require high chip counts or feedback control systems. Consequently, hot swap methods that are currently available are complex, area consuming, and expensive.